1. Field of Invention
Psoralens, photochemotherapy, psoralens having enhanced photosensitizing activity for use in photochemotherapy.
2. Prior Art
Psoralens have been used for years as dermalphotosensitizing agents, e.g., in the treatment of vitiligo. Their topical and/or oral application, followed by irradiation with light, results in stimulation of melanin, thus producing a tanning effect. They have accordingly also been used for such cosmetic purpose. More recently, psoralens have been found useful in the photochemotherapeutic treatment of psoriasis, in which case they are administered orally or topically to the subject, whose skin is subsequently exposed to controlled ultraviolet radiation, as in a Psoralite (TM) apparatus. A high percentage of remissions of this disease have been effected in such manner.
The effectiveness of a psoralen for such uses and for such purpose is related to its ability to produce erythema upon the skin upon irradiation. Psoralens also have other uses, and their uses, as well as underlying rationale and theory, are partially elucidated in U.S. Pat. No. 4,124,598, and are otherwise well-known in the art from various preexisting publications.
With the increasing emphasis on photochemotherapeutic treatments for various purposes using psoralens and controlled application of ultraviolet light, the requirements for optimally-effective photosensitizing psoralens have become more apparent. To eliminate the necessity of excessive and perhaps dangerous ultraviolet light applications or dosages, maximum photosensitization is one obvious criterion. However, to eliminate excessive periods of waiting before photochemotherapy can be commenced, rapid onset of photosensitization upon topical or oral administration of the photosensitizing agent is also of significance. Perhaps an even more important criterion is rapid decline in photosensitizing activity of the photosensitizing agent after reaching maximum and/or effective photosensitization levels after administration. Obviously, if the photosensitization effect does not decline relatively rapidly, or at least within a reasonably limited period after maximization, a patient must be confined for uneconomic and undesirable periods after treatment so that photosensitization does not continue after the desired ultraviolet light treatment period, with the distinct danger of excessive and undesirable continuance of photochemotherapy because of exposure to normally-encountered light rays upon leaving the treatment area. Thus, the criteria of rapid onset, early maximization, and rapid decline of photosensitization effect have already become established as desirable criteria for the photosensitizing agents in this relatively new but rapidly-expanding field of photochemotherapy, certainly of equal importance as contrasted to the single previously-important criterion of high maximum photosensitization activity alone.
Although some psoralens, such as trimethylpsoralen (4,5',8-trimethylpsoralen or trioxsalen) are characterized by considerable topical activity, they have a diminished order of oral activity, or at least the oral activity is a modicum for purposes of practical photochemotherapeutic utilization. In contrast, 8-methoxypsoralen is characterized by significant oral activity. The psoralen compounds of U.S. Pat. Nos. 4,124,598 and 4,130,568 are also characterized structurally by the presence of an 8 carbon atom substituent, e.g., an 8-methoxy or 8-methyl substituent, which has heretofore apparently been considered desirable for substantial photosensitizing activity, whether oral or topical, of course along with other substituents present in the 4',4, and 5' positions, in those prior art psoralen compounds which have heretofore been found to have desired photochemotherapeutic activity.